Yanmar 3HM35F Specifications
| Engine Model: Yanmar 3HM35F |
| Engine Type: 4-stroke inline 3-cylinder naturally aspirated water-cooled diesel |
| Total Displacement: 78.2 cu.in (1.28 L) |
| Rated Engine Power: 34.1 Hp (25.4 kW) at 3400 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 3HM35F is the freshwater-cooled
variant of the 3HM35 marine diesel engine, distinguished by its heat
exchanger cooling system that allows operation in saltwater environments
without exposing the engine block to corrosion. This heavy-duty,
three-cylinder engine is part of Yanmar’s HM series, produced from 1983
to 1992, and is known for its cast iron construction and high torque
output suitable for larger sailboats, workboats, and auxiliary marine
propulsion. The Yanmar 3HM35F features indirect injection with a swirl
pre-combustion chamber, a design that provides smooth operation, reduced
combustion noise, and reliable cold-start performance.
The engine is naturally aspirated, relying on its robust displacement
for power delivery. The freshwater cooling system incorporates a heat
exchanger that isolates the engine’s internal coolant circuit from the
raw seawater used for heat rejection, extending engine life in marine
service. The 3HM35F is commonly paired with the KM3P mechanical cone
clutch transmission, making it a popular choice for displacement hull
vessels requiring reliable auxiliary power.
The Yanmar 3HM35F is a four-stroke, water-cooled diesel engine operating
on the compression-ignition principle. The engine architecture is an
inline three-cylinder configuration with a total displacement of 1.282 L
(78.23 cu.in), derived from a bore of 80 mm (3.15 in) and a stroke of 85
mm (3.35 in). This undersquare design promotes torque generation at low
engine speeds, a characteristic essential for marine propulsion where
sustained propeller loading is required. The combustion system utilizes
indirect injection with a swirl pre-combustion chamber.
Two distinct power ratings are specified for continuous versus maximum
operation. The maximum output for intermittent operation is 25.4 kW
(34.1 hp) at 3,400 rpm. The continuous output rating is 22.4 kW (30 hp)
at 3,200 rpm. These dual ratings allow the engine to deliver full power
for short durations (maneuvering) while operating at reduced output for
extended cruising. The idle speed is set at 850 rpm. The governor is a
mechanical centrifugal flyweight type.
The cylinder block is manufactured from cast iron with a vertical,
inline three-cylinder configuration. The heavy-duty cast iron
construction provides the rigidity and wear resistance required for
sustained marine duty cycles where continuous operation at moderate
loads is common. The cylinder bores are cast directly into the block and
finished with a plateau honing process that optimizes oil retention and
piston ring sealing.
The crankcase is reinforced to minimize distortion under thermal and
mechanical stress. The main bearing housing is an integral part of the
block casting. The oil pan (lubricating oil sump) is mounted at the
lower section of the engine. A cast aluminum timing gear housing sits at
the front of the block.
The cylinder head is manufactured from cast iron, matching the cylinder
block material to ensure uniform thermal expansion. The valvetrain is an
overhead valve (OHV) configuration with the camshaft located in the
cylinder block, driven by the front gear train. Each cylinder utilizes
two valves - one intake and one exhaust.
Valve clearances require periodic mechanical adjustment. The cold valve
clearance is set at 0.2 mm (0.008 in) for both intake and exhaust
valves. The valve seat inserts are manufactured from heat-resistant
alloys selected for diesel operation durability.
The cylinder head incorporates the intake manifold mounting flange,
exhaust manifold mounting flange, and the fuel injector ports positioned
for the swirl pre-combustion chamber. A bonnet (valve cover) seals the
top of the cylinder head. A decompression mechanism is provided for
manual engine starting.
The 3HM35F is equipped with a mechanical indirect injection (IDI) fuel
system. A camshaft-driven in-line injection pump pressurizes fuel and
delivers it to the injectors. The injection pump features a mechanical
governor that controls fuel delivery based on engine speed and load. The
injection pump is lubricated by the engine oil system through a
connection at the gear housing. The pump can be removed for service
after disconnecting fuel lines and securing bolts, with careful
attention required to manage the cam followers during reinstallation.
The injection lines are high-pressure steel tubes routed individually
from the injection pump to the injectors mounted in the cylinder head.
The injectors are of the throttle-type nozzle design, incorporating a
spring-loaded pintle nozzle. The injection pressure is set at 160-170
kg/cm2 (15.7-16.7 MPa / 2,275-2,420 psi). A fuel feed pump (lift pump)
supplies fuel from the tank to the injection pump. A fuel strainer
provides primary filtration before the feed pump. A fuel return pipe
recirculates excess fuel to the tank.
The lubrication system is a forced-feed design utilizing a gear-driven
trochoid-type oil pump. The oil pump is mounted within the front gear
housing and driven by the camshaft gear train. The system draws
lubricant from the sump through a strainer (oil intake screen) and
delivers it to the main oil gallery. A pressure regulating valve
maintains stable system pressure within the specified range. The engine
employs a full-flow spin-on oil filter mounted on the engine block.
The total oil capacity (sump plus filter) is 5.4 L (5.7 US qt). Note
that complete evacuation of all oil during changes is not achieved with
suction pumps, and the dipstick level must be used as the final fill
reference. The engine requires SAE 15W-40 diesel engine oil meeting API
CD or higher specification. A lubricating oil dipstick is provided for
level checking.
The 3HM35F utilizes an indirect freshwater cooling system with a heat
exchanger, which distinguishes it from the raw-water-cooled 3HM35 model.
The system maintains fresh coolant within the engine block while raw
seawater passes through the heat exchanger to reject heat overboard. The
fresh water pump is gear-driven from the engine front cover. The raw
water pump is a separate gear-driven unit mounted on the front of the
engine.
The cooling system includes a freshwater cooler (heat exchanger) where
heat transfer occurs between the engine coolant and seawater. A
thermostat regulates coolant temperature by controlling flow through the
heat exchanger. The system includes an expansion tank (sub-tank) to
accommodate coolant volume changes. A mixing elbow combines exhaust
gases with cooling water discharge to reduce exhaust temperatures in the
engine compartment. The coolant capacity is 6.5 L (with heat exchanger).
The recommended coolant mixture is a 50/50 glycol-water blend.
| Intake and Exhaust Systems |
Air Intake: The intake system employs a suction silencer (air intake
silencer) to reduce induction noise. The engine is naturally aspirated,
drawing air through the silencer directly into the intake manifold.
Exhaust System: The exhaust system incorporates a water-cooled exhaust
manifold that injects cooling water into the exhaust stream and a mixing
elbow that further cools exhaust gases before discharge. The exhaust
outlet pipe diameter is 50 mm (2.0 in). The manifold and cover are
accessible for cleaning carbon deposits during maintenance.
The electrical system is 12V with a 1.2 kW (1.6 hp) starter motor and a
55A alternator as standard equipment. A higher-output 60A alternator was
available as an option. The system includes wire harness and battery
connections.
Engine Management: The 3HM35F utilizes no electronic engine management
system. Fuel delivery is controlled mechanically by the injection pump
governor. A mechanical engine stop device shuts off fuel supply via a
cable or lever. An idle adjuster allows mechanical idle speed setting.
The engine can be controlled via speed remote control cable.
Transmission (KM3P): The engine is commonly paired with the Yanmar KM3P
mechanical cone clutch transmission. Gear reduction ratios vary by
propeller requirements. Forward ratios available include 2.36:1, 2.61:1,
and 3.20:1. The reverse ratio is 3.04:1.
Several dimension and weight specifications exist for the 3HM35F
depending on included components and measurement methods. Dry weight
(with KM3P gear): 184 kg (406 lbs). Length is 808 mm (31.8 in), width is
480 mm (18.9 in), and height is 613 mm (24.1 in). The vessel application
listing confirms the engine’s physical fit in a 40-foot sailing yacht.
These compact dimensions allow installation in engine compartments of
sailboats and small workboats where space is at a premium.
The service life of the 3HM35F under proper operating conditions is
engineered to exceed 8,000 operating hours in marine auxiliary service
with regular maintenance. Oil change intervals are recommended at 150
operating hours for severe service or 250 hours under normal operating
conditions. The engine requires SAE 15W-40 diesel engine oil meeting API
CD or higher specification. The total oil capacity is 5.4 L (5.7 US qt)
with filter.
Valve clearance inspection and adjustment is mandated every 500
operating hours. The cold valve clearance is set at 0.2 mm (0.008 in)
for both intake and exhaust valves. Replacement of the fuel filter is
required every 500 operating hours. The fuel strainer should be cleaned
at the same interval. Raw water pump impeller replacement is recommended
every 200-500 operating hours depending on usage. The air cleaner
requires servicing based on operating environment.
The coolant must be replaced every 2 years or 2,000 operating hours,
using a 50/50 glycol-water mixture. The zinc anodes in the heat
exchanger and raw water circuit require inspection every 250 operating
hours. Common maintenance procedures include removing the exhaust
manifold cover to clean carbon deposits from the exhaust manifold. When
servicing the injection pump, removal requires either removing the pump
before the gear case or manually rotating the engine to reposition cam
lobes for follower clearance.
The cylinder head bolts are torqued to 90 Nm (66 lb-ft) in a specified
sequence from the center bolts outward. The connecting rod cap nuts are
torqued to 50 Nm (37 lb-ft). The main bearing cap bolts are torqued to
65 Nm (48 lb-ft).
The flywheel-to-crankshaft bolts receive a torque of 80 Nm (59 lb-ft).
The rocker arm shaft pedestal bolts are torqued to 25 Nm (18 lb-ft). The
injection pump drive gear bolt is torqued to 35 Nm (26 lb-ft). The
injector hold-down nuts are torqued to 25 Nm (18 lb-ft).
The intake and exhaust manifold bolts are torqued to 30 Nm (22 lb-ft).
The exhaust manifold cover retaining nuts are torqued to 20 Nm (15
lb-ft). The glow plugs are torqued to 15 Nm (11 lb-ft). These values
assume the use of high-strength, lubricated threads as per factory
specifications.
The Yanmar 3HM35F is exclusively a marine propulsion engine designed for
auxiliary power in larger sailboats and primary power in workboats. The
engine is suitable for vessels in the 30- to 45-foot length range, with
documented installation in a 40-foot Frers Carroll Marine 41 sailing
yacht. The engine provides sufficient power for displacement hull
cruising at speeds of 6-7 knots.
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